MD Settings: Remove some ES6 leftovers from CrOS code that break uglify.

chrome/browser/resources/settings/device_page/display.js

Index: chrome/browser/resources/settings/device_page/display.js
diff --git a/chrome/browser/resources/settings/device_page/display.js b/chrome/browser/resources/settings/device_page/display.js
index 31e25c81631220715146a2a2600aa36d837f94e8..1a9a8c98e22b1639bd8c340b1e6e69d5298c263c 100644
--- a/chrome/browser/resources/settings/device_page/display.js
+++ b/chrome/browser/resources/settings/device_page/display.js
@@ -118,7 +118,7 @@ Polymer({
    * @param {!Array<!chrome.system.display.DisplayUnitInfo>} displays
    * @private
    */
-  displayInfoFetched_(displays) {
+  displayInfoFetched_: function(displays) {
     if (!displays.length)
       return;
     settings.display.systemDisplayApi.getDisplayLayout(
@@ -130,7 +130,7 @@ Polymer({
    * @param {!Array<!chrome.system.display.DisplayLayout>} layouts
    * @private
    */
-  displayLayoutFetched_(displays, layouts) {
+  displayLayoutFetched_: function(displays, layouts) {
     this.layouts = layouts;
     this.displays = displays;
     this.updateDisplayInfo_();